Computer tomography (CT) is a high resolution imaging technique that has relatively low inherent contrast resolution in soft tissue structures such as the liver, spleen, pancreas and kidneys. More than 62 million CT scans are performed each year in the United States in about 7,200 facilities, and approximately 40 million of these procedures require the intravenous administration of iodinated contrast material. In order to be effective, the iodinated contrast material is administered intravenously as a bolus infusion (not a drip infusion) for most clinical indications. The exceptions would include the search for acute hemorrhage or calculi, particularly in the genitourinary tract, when intravenous contrast material is not necessary and in some cases contraindicated.
When administering iodinated contrast material as a bolus, it is typically delivered via a power injector that is programmed prior to the CT acquisition. That is, the volume, rate and pressure of administration are preset before delivering the contrast material and subsequently acquiring the CT scan. For example, 150 ml of a contrast agent would be administered at 5 ml/sec with a maximum pressure of 300 pounds per square inch (PSI). However, in some cases, the use of a power injector results in the extravasation of the iodinated contrast compound (i.e., leakage outside the vein into the surrounding soft tissue). Such incidents result in unreliable and/or ineffective CT scans as well as adverse effects on the patient, such as skin ulcerations and compartment syndrome, which require additional medical attention.
Although some power injectors use devices to detect the extravasation of contrast material (e.g., EZ-EM, MedRad), the technologists or nurses responsible for administering the contrast media bolus frequently encounter a scenario where they are uncomfortable or wary of using the power injector. Typical scenarios that may be problematic include: (1) poor or tenuous intravenous access; (2) use of an existing IV line in an in-patient that has been in place for several days; (3) injection of a central venous catheter through which many hospitals have policies prohibiting power injection; and (4) injection of children. When one or more of these scenarios occurs, contrast material is typically administered via a hand injection. That is, the technologist or nurse administers the contrast material by hand with one or more syringes. Since the volumes of contrast material used for CT are typically in the 125-150 ml range, and because larger volume syringes require more force to push the plunger, the contrast material is typically divided up into several smaller syringes. For example, rather than injecting 150 ml of contrast material via a 150 ml syringe, the technologist or nurse may inject 25 ml through six different 25 ml syringes. This problem is further exacerbated by the fact that contrast agents with higher concentrations of iodine (e.g., 370 mg/ml rather than 300 mg/ml) are becoming increasingly popular in the era of fast, multidetector CT scanners. The contrast agents with higher concentrations of iodine have a much higher viscosity, making them even more difficult to inject by hand. Although administering the bolus via several small volume syringes is much easier for the individual performing the injection, the episodic delivery of contrast material (e.g., inject 25 ml, disconnect the empty syringe, reconnect a full syringe, inject more contrast material, etc.) results in a suboptimal vascular and tissue enhancement profile.
This administration scheme is not compatible with the goal of having vivid and sustained vascular and tissue enhancement during the CT acquisition. As a result, certain subtle but critical disease processes such as hepatic, pancreatic or renal tumors may be missed. Furthermore, other protocols such as CT angiography cannot be performed using a hand injection, since certain diagnoses, such as pulmonary embolism, rely on very vivid vascular enhancement. In summary, the use of hand injection reduces the risk of contrast media extravasation into the perivenous soft tissue but results in a suboptimal CT scan from a diagnostic standpoint.
Moreover, the catheters currently used to inject the contrast media in the patient can cause extravasation. As described above, because the contrast media must be administered as a bolus, these catheters produce a jet at the catheter tip, which can result in extravasation of the contrast media into the surrounding soft tissue of the patient. For example, vessel wall perforation may be caused by the contrast media jet exiting the aperture at the tip of a typical catheter. For this reason, the flow rate of the contrast media may have to be reduced, requiring a longer time to deliver the fluid.
The present disclosure addresses these current problems in the field of computer tomography imaging.